Thermoplastic polyester compositions, such as poly(alkylene terephthalates), have valuable characteristics including strength, toughness, high gloss, and solvent resistance. Polyesters therefore have utility as materials for a wide range of applications, from automotive parts to electric and electronic appliances. Because of their wide use, particularly in electronic applications, it is desirable to provide flame retardancy to polyesters. One set of test conditions commonly accepted and used as a standard for flame retardancy is set forth in Underwriters Laboratories, Inc. Bulletin 94, which prescribes certain conditions by which materials are rated for self-extinguishing characteristics. Another set of conditions commonly accepted and used (especially in Europe) as a standard for flame retardancy is the Glow Wire Ignition Test (GWIT), performed according to the International standard IEC 695-2-1/2.
Numerous flame retardants for polyesters are known, but many contain halogens, usually chlorine and/or bromine. Halogenated flame retardant agents are less desirable because of the increasing demand for ecologically friendly ingredients. Halogen-free flame retardants, such as phosphorus- and nitrogen-based compounds can be used as well. Unfortunately, they lack good flame retardancy in thin sections.
There is a need for polyester compositions having the combination of good flame retardant properties not only at thicknesses of 1.5 mm or greater, but also at thicknesses of 0.8 mm or less. It would be advantageous if this combination of flame retardant properties could be achieved while at least essentially maintaining mechanical properties and/or heat properties.